When Australian lawyer Mathew Alderson's two young children want to share a secret, they instinctively switch to rapid-fire Putonghua, confident that neither of their parents will be able to fully follow the conversation.
After the family moved to Beijing two years ago, Alderson and his wife, Sasha, decided that enrolling their children in local schools - where little or no English is spoken - would be the best way for them to learn Chinese. The youngsters were bewildered at first but quickly adapted. Nik, seven, recently scored top marks on a language test, and Natalia, four, speaks better Putonghua than English, her parents say.
The Aldersons - and many other expatriate families - realise that a posting in China offers their children the chance to achieve fluency in a language that is becoming increasingly important, as its economy could well overtake that of the United States as the world's largest in the next decade.
Choosing a mainland school generally means spartan classrooms, rote learning methods and rigid discipline. But Alderson and his wife reckon these are more than compensated for by their offspring achieving a linguistic skill that will be a major professional asset in their lifetime.
There is also the matter of money. Fees at state-run schools can be as low as HK$25,000 a year, significantly less than those at an international school. For expatriates without generous packages from their employers, enrolling in an international school in the capital is simply not an affordable option.
Teenage student Hayley Downes, who has Canadian and Australian citizenship, has been educated in both systems. After arriving from Australia, she attended the Beijing City International School before switching more than a year ago to the state-run Middle School No 55, a move intended to improve her Chinese-language skills.